Thermoelectric device

ABSTRACT

The present invention is a thermoelectric device comprising: a thermoelectric element composed of principally thermoelectric material, a counter element adhered to said thermoelectric material, a solder layer lying between said thermoelectric element and said counter element and adhering said thermoelectric element to said counter element, a restraining layer to prevent said solder&#39;s ingredient of said solder layer from spreading into said thermoelectric element, wherein said restraining layer comprising a first layer to prevent said solder&#39;s ingredient of said solder layer from spreading into said thermoelectric element and a second layer composed of material which gets wetter than said first layer against said solder layer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a thermoelectric devicecomprising a thermoelectric element composed of principallythermoelectric material.

[0003] 2. Discussion of the Background

[0004] The thermoelectric device comprising a thermoelectric elementprincipally composed of thermoelectric material is well known in theart.

[0005] The thermoelectric device has two types of usages one is acool-heat type which can cool or heat when electricity being supplied,and the other is a power generation type which can generate electricitywhen being cooled or heated.

[0006] A known conventional thermoelectric device is disclosed in pages24 to 25 of “thermoelectric transfer system technical general handbook”published by realize company published date; on June 30, June, 1995(heisei 7).

[0007] The nickel plating layer prevents the solder's ingredient of saidsolder layer from spreading into the thermoelectric element, andconsists of a single layer. According to the conventional thermoelectricdevice, the nickel plating layer prevents the solder's ingredient of thesolder from spreading into said thermoelectric element. Therefore, theconventional thermoelectric device has advantages of restraineddegradation of thermoelectric device and maintained characteristic ofthermoelectric device for long term.

[0008] Furthermore, in general, the thermoelectric element composed ofthermoelectric material is hard to be soldered. The nickel plating layerhas an advantage to prevent the solder's ingredient of the solder layerfrom spreading into the thermoelectric element, and improve a solderingcharacteristic of the thermoelectric element when the thermoelectricelement being assembled.

[0009] In the industry, the higher characteristic of restraining spreadprevention and soldering are requested. However, the single nickelplating layer needs more improvement in aspect of combining two highercharacteristics of spread prevention and soldering. In other words, ifthe nickel plating layer is used for high characteristic of spreadprevention, it has an advantage to prevent solder's ingredient of thesolder layer from spreading into the inside of the thermoelectricelement, but then it has disadvantage to get insufficient increasewetting property against the solder. Contrary, if the nickel platinglayer is used for the high wetting property against the solder, it isnot sufficient to increase the increasing of the characteristic ofspread prevention.

[0010] An object of the present invention is to solve theabove-mentioned disadvantages, and more specifically, to provide athermoelectric device having both improvements for better solderingproperty and spread prevention.

SUMMARY OF THE INVENTION

[0011] The present invention is a thermoelectric device comprising: athermoelectric element composed of principally thermoelectric material,a counter element adhered to said thermoelectric material, a solderlayer lying between said thermoelectric element and said counter elementand adhering said thermoelectric element to said counter element, arestraining layer to prevent said solder's ingredient of said solderlayer from spreading into said thermoelectric element, wherein saidrestraining layer composed a first layer to restrain what said solder'singredient of said solder layer spreads into said thermoelectric elementand a second layer composing of material which gets wetter than saidfirst layer against said solder layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and other objects, features and advantages of thepresent invention will be more apparent and more readily appreciatedfrom the following detailed description of preferred exemplaryembodiments of the present invention, taken in connection with theaccompanying drawings, in which:

[0013]FIG. 1 is front view showing an outline structure of athermoelectric device according to an embodiment of the presentinvention.

[0014]FIG. 2 is a schematic cross sectional view of substantial part ofa thermoelectric device according to the embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] According to the present invention, the thermoelectric materialfor the thermoelectric device is at least one of selected frombismuth-tellurium series, bismuth-selenium series, antimony-telluriumseries, antimony-selenium series, bismuth-tellurium-antimony series, andbismuth-tellurium-selenium series. Specifically, it is at least one ofselected from Bi₂Te₃, Bi₂Se₃, Sb₂Te₃, Sb₂Se₃. Bismuth-tellurium-antimonyseries is selected for a thermoelectric device of P-type (positivetype). Bismuth-tellurium series and bismuth-tellurium-selenium seriesare selected for a thermoelectric device of N-type (negative type).

[0016] According to the present invention, the counter element adheredto the thermoelectric element is a substrate having an electrode. Aceramic substrate may be employed for the substrate. A ceramic materialis selected from alumina series, aluminum nitride series, beryllia (BeO)series, and silicon carbide series etc. A solder may be selected frombismuth-tin series, tin-antimony series, lead-tin series,lead-tin-bismuth series, tin series, and lead series etc., but thesolder is not limited to aforementioned series.

[0017] According to the present invention, the restraining layercomprises a first layer to prevent the solder's ingredient of saidsolder layer from spreading into the thermoelectric element and a secondlayer composed of material which gets wetter against the solder layerthan the first layer. The first layer is nonelectrolytic plating layercomposed of nickel-phosphorus series, or non-electrolytic plating layercomposed of nickel series. The second layer has preferably bothimprovements of wetting property against the solder. A second layercomprised a non-electrolytic plating layer composing of nickel-boronseries. A non-electrolytic plating layer composed of nickel-boron seriesis slower in the plating speed and more expensive in manufacturing thana non-electrolytic plating layer composed of nickel-phosphorus series.However, nickel-boron has excellent wetting property against the solderwhen soldering, so that the soldering characteristic of thethermoelectric device is improved.

[0018] A non-electrolytic plating layer composed of nickel-phosphorusseries is a little degradation in the wetting property, but is faster inthe plating speed and cheaper in manufacturing than a nonelectrolyticplating layer composing of nickel-boron series.

[0019] A non-electrolytic plating layer composing of nickel-phosphorusseries is produced by the plating bath including, but not limited tonickel-chloride or hydrosulfate, with sodium hypophosphite as thereducer. A non-electrolytic plating layer composing of nickel-boronseries is produced by plate bath including, but not limited to,nickel-chloride or hydrosulfate with boron hydroxylase as the reducer.

[0020] In some cases, the first layer and the second layer do notlimited by non-electrolytic plating, and these can be produced byelectroplating of nickel metal etc.

[0021] According to the present invention, the average thickness of thefirst layer is thicker than that of the second layer to increase thespread prevention effect at low cost by the short time process. Though aratio of the average thickness between the first layer, and the secondlayer is varied by consideration of manufacturing speed or manufacturingcost under usable conditions, it may be settled for “the average of thefirst layer: the average of the second layer=1: (1 to 300)”. Preferably,it may be settled for “the average of the first layer: the average ofthe second layer=1: (1 to 100)”. More preferably, it may be settled for“the average of the first layer: the average of the second layer=1: (2to 10)”. However, the present invention is limited by theaforementioned.

[0022] A ratio of raw value of the average thickness between the firstlayer and the second layer is varied by consideration of manufacturingspeed, manufacturing cost under usable conditions, or material of thefirst layer or the second layer etc. Accordingly, in some cases, forexample, the average of the first layer is settled for 0.2 to 50 μm, 0.5to 20 μm, 1.0 to 15 μm, 1.0 to 10 μm, and 5 to 10 μm etc. The average ofthe second layer is settled for 0.04 to 10 μm, 0.8 to 5 μm, 0.1 to 1.0μm, and 0.1 to 0.5 μm etc. However, the present invention is not limitedby the aforementioned ratio of them.

EMBODIMENT EXAMPLE

[0023] Preferred embodiments of the present invention will be describedhereinafter in detail with reference to the accompanying drawings.

[0024]FIG. 1 is a front view showing an outline structure of athermoelectric device according to the embodiment of the presentinvention. FIG. 2 is schematic cross sectional view of a thermoelectricdevice according to the embodiment of the present invention. As shown inFIG. 1, the thermoelectric device related to the present inventioncomprises the thermoelectric modules, which are the thermoelectricelement 1, the counter element 3 countered each other, and the solderlayer 5 to adhere the thermoelectric element 1 and the counter element 3each other.

[0025] The counter element 3 comprises a pair of insulative ceramicsubstrata (material: alumina) 30, 31 having the planes 30 c, 31 c formounting the elements countered each other and the conductive electrodes(material: copper) 35 lain between said planes 30 c, 31 c and the solderlayer 5.

[0026] The solder 5 is composed of conductive, and low melt point metal.The solder 5 is composed of tin-antimony alloy.

[0027] The thermoelectric material for the thermoelectric element 1converts electric energy into heat energy, or heat energy into electricenergy, and the material is composed of one of selected frombismuth-tellurium series, bismuth-selenium series, antimony-telluriumseries, and antimony-selenium series. The aforementioned thermoelectricmaterial has naturally poor wetting property against the solder whensoldering. Furthermore when used for the thermoelectric device, thesolder's ingredient composed of the solder layer 5 is apt to spread intothe inside of the thermoelectric element 1 by heat-influences. If thethermoelectric device is used for long time, the spread brings thedegradation of the thermoelectric element 1 and the conductive defect.

[0028] According to the present invention, in order to improve thecharacteristic of soldering and prevent the degradation of thethermoelectric element 1 due to the spread of the solder's ingredient,the restraining layer 7 lies between the thermoelectric element 1 andsolder layer 5 as shown in FIG. 2 to prevent the solder's ingredientconsisting the solder layer 5 from spreading into the inside of thethermoelectric element 1.

[0029] The restraining layer 7 related to the present inventioncomprises two-layer composition of the first layer 71 (the averagethickness: 0.5 to 10.0 μm) and the second layer 72 (the averagethickness: 0.1 to 1.0 μm). The first layer 71 has the conductivecharacteristic, and a main object of the first layer 71 is to preventthe solder's ingredient of the solder layer 5 from spreading into theinside of the thermoelectric element 1. Furthermore, the first layer 71lies between the end face 1 a of the thermoelectric element 1 and thesecond layer 72 so that it counters directly to the plain end face 1 aof the thermoelectric element 1 which is the physical object to beprevented from the spreading phenomenon. Specifically, the first layer71 comprises the non-electrolytic plating layer composed ofnickel-phosphorus series. The average of the thickness of the firstlayer 71 is thicker than that of said second layer 72.

[0030] The second layer 72 has conductive characteristic and an mainobject of the second layer 72 is to provide better wetting propertyagainst the solder layer than said first layer 71 when soldering.Therefore, the second layer 72 lies between the solder 5 and the firstlayer 71 so that it counters directly to a solder layer 5. Accordingly,the second layer 72 composed of the better wetting property than thefirst layer 71 against the solder. Specifically, the second layer 72comprises the non-electrolytic plating layer composed of nickel-boronseries.

[0031] As shown in FIG. 1, the distinction of P-type and N-type of eachthermoelectric element 1 is labeled as “P”, and “N”. When thethermoelectric device is used, the electrode 35A (35) of one end side isconnected to a plus pole of a power supply, and the other end side isconnected to a minus pole of power supply through the pluralthermoelectric elements including the electrode 35B (35) is connected,so that electric power is fed between the plus pole of and the minuspole of the power supply. Therefore, the substrate 30 of the one side iscooled to be the low temperature side, and the substrate 31 of the otherside is heated to be the high temperature side due to the thermoelectriceffect of the each thermoelectric element.

[0032] Alternatively, the low temperature and the high temperature sidesare reversed when switching the plus pole and the minus pole to feedelectric power in the revered direction.

EXAMPLE OF EMBODIMENT

[0033] The thermoelectric device shown in FIG. 1 and FIG. 2 was used forthe test piece. The first layer 71 composed of the non-electrodenickel-phosphorus plate layer (phosphorus is 2 to 8 wt %) was laminatedon the both end sides la of the thermoelectric element 1 by the firstnon-electrode plating procedure. Furthermore, the first layer 72composed of the non-electrode nickel-boron plate layer (boron is 1 wt %)was laminated on the first layer 71 by the second nonelectrode platingprocedure.

[0034] The three kinds of the first layer 71 were prepared for theevolution with the thickness of 0.5 to 1.0 μm, 1.0 to 5.0 μm and 5.0 to10.0 μm. The two kinds of the second layer 72 were also prepared withthe thickness of 0.1 to 0.5 μm and 0.5 to 1.0 μm.

[0035] In order to evaluate the defect of soldering, the burn-in testwhich fed electric current of 2 [A] to each test piece was performed.After the burn-in test the cool-heat test was performed to hold the testpieces at the temperature of −40° C., for 15 minutes and at thetemperature of 80° C. for 15 minutes. The variation ratio of innerelectrical resistance of the test pieces were measured before and afterthe burn-in test and the cool-heat test. If the alteration ratio ofinner electrical resistance is not more than 0.5%, the test piece isevaluated as an acceptable product. If the alteration ratio of innerelectrical resistance exceeds 0.5%, the test piece is evaluated as anacceptable product. 30 test pieces were prepared, and the rate ofoccurrence for non-acceptable product among thirty (30) test pieces werecalculated.

[0036] Furthermore, the other test pieces were tested by the hightemperature exposure test to maintain the temperature the test pieces at150° C. Accordingly, the variation ratio of inner electrical resistanceof the test pieces were measured before and after the high temperatureexposure test. If the alteration ratio of inner electrical resistance isnot more than 10%, the test piece is evaluated as an acceptable product.If the alteration ratio of inner electrical resistance exceeds 10%, thetest piece is evaluated as a non-acceptable product. 22 test pieces wereprepared, and the rate of occurrence for non-acceptable product among 22test pieces were calculated.

[0037] Table 1 shows results of the evaluation concerning the embodimentexamples.

[0038] In the same way as the present embodiment example, as the testpiece related to the comparative example 1, the first layer 71 composedof the non-electrode nickel-phosphorus plate was laminated with thethickness of 1.0 to 5.0 μm on the end side of the thermoelectric element1. The thermoelectric device was produced as the same way asabove-mentioned, and was evaluated as the same way as theabove-mentioned test example. As the test piece related to thecomparative example 2, the first layer 71 composed of the non-electrodenickel-phosphorus plate was laminated with the thickness of 0.5 to 1.0μm on the end side of the thermoelectric element 1. The thermoelectricdevice was produced as the same way as above-mentioned, and wasevaluated as the same way of as the above-mentioned test example.

[0039] Regarding the test pieces of the comparative example 1 and thecomparative example 2, the first layer 71 composed of non-electrodenickel-phosphorus plate was laminated, but the second layer 72 composedof non-electrode nickel-boron plate was not laminated.

[0040] Table 1 shows results of the evolution concerning the comparativeexample 1 and the comparative example 2.

[0041] Regarding the test piece related to the embodiment example, thesecond layer 72 composed of the nonelectrode nickel-boron plate layerwith good wetting property against the solder is laminated on the firstlayer 71 composed of the non-electrode nickel-phosphate plate layer withthe high spread prevention property. Therefore, this embodiment examplehad the spread property to prevent solder's ingredient from spreadinginto the inside of the thermoelectric element 1, and had improvedsoldering characteristic for electrode 35 and thermoelectric element 1,and had restrained degradation of the test piece after each test.

[0042] Consequently, as understood in Table 1, according the test piecesfrom the embodiment example, the rate of occurrence of defective testpieces were zero or extremely low.

[0043] As shown in Table 1, under the aforementioned test condition,when the thickness of the first layer 71 was 0.5 to 1.0 μm, the rate ofoccurrence of defective test pieces after the high temperature exposuretest was {fraction (3/22)} (three per twenty-two). Considering thisresult, under the aforementioned test condition, the preferablethickness of the first layer 71 is no less than 1.0 μm. Furthermore, ifthe test condition of the thermoelectric device is loosened, thethickness of the first layer 71 of no more than 1.0μ is satisfied as anon-defective test piece.

[0044] According to the present invention, when the first layer is anon-electrolytic plating layer composed of nickel-phosphorus series, andthe second layer is non-electrolytic plating layer composed ofnickel-boron series, the present invention is able to achieve the goodeffect.

[0045] According to the present invention, when the average thickness ofthe first layer is thicker than that of said second layer, the solder'singredient is effectively prevented from spreading into thethermoelectric element. Specially, when the average thickness of thefirst layer composed of nickel-phosphorus series is thicker than that ofthe second layer composed of nickel-boron series, the present inventionmay efficiently achieve the spread prevention effect, may increase theproductivity and may achieve low cost in manufacturing due to the thinnon-electrolytic plating layer composed of nickel-boron series whoseplating speed is slow and expensive in manufacturing. TABLE 1Comparative Comparative Embodiment example Example 1 Example 2 Secondlayer Ni—B Thickness (μm) 0.1˜0.5 0.5˜1.0 — — First layer Ni—P Thickness(μm) 0.5-1.0 1.0-5.0 5.0-10.0 0.5-1.0 1.0-5.0 5.0-10.0 1.0-5.0 0.5-1.0Defect ratio after the burn- 0/30 0/30 0/30 0/30 0/30 0/30 4/30 5/30 intest and the cool-heat test High temperature exposure 3/22 0/22 0/220/22 0/22 0/22 0/22 9/22 test Defect ratio after 30-hours Hightemperature exposure 0/22 0/22 0/22 0/22 0/22 0/22 0/22 2/22 test Defectratio after 10-hours

1. A thermoelectric device comprising: a thermoelectric element composedof principally thermoelectric material, a counter element adhered tosaid thermoelectric material, a solder layer lying between saidthermoelectric element and said counter element and adhering saidthermoelectric element to said counter element, a restraining layer toprevent solder's ingredient of said solder layer from spreading intosaid thermoelectric element, wherein said restraining layer comprising afirst layer to prevent said solder's ingredient of said solder layerfrom spreading into said thermoelectric element and a second layercomposed of material which gets wetter than said first layer againstsaid solder layer.
 2. A thermoelectric device according to claim 1 :wherein said first layer is a non-electrolytic plating layer composed ofnickel-phosphorus series, and said second layer is non-electrolyticplating layer composed of nickel-boron series.
 3. A thermoelectricdevice according to claim 1 : wherein the average of the thickness ofsaid first layer is thicker than that of said second layer.
 4. Athermoelectric device according to claim 2 : wherein the average of thethickness of said first layer is thicker than that of said second layer.